Organic walnut farmers work to control orchard pests

Acreage of organic walnuts has increased, and with this increase comes a need for effective pest management practices. The three main pests are navel orangeworm, walnut husk fly and codling moth.

Ryan Fillmore, vice president of operations for Fillmore Farms in Gridley, raises organic walnuts and operates a walnut sheller, which processes nuts for the farm and for other organic growers.

The navel orangeworm is a major pest for Fillmore, and he said codling moth and walnut husk fly can also be a bit challenging, because the organic treatment methods are generally more expensive and less effective.

"I'm quite interested in doing some of the mating disruption this next year for the navel orangeworm. Trécé has a kairomone pheromone organically certified mating-disruption product that I'm looking at," Fillmore said, adding there's also a puffer that releases pheromones for mating disruption that he's interested in and will be testing in the 2021 season.

Fillmore said he has done some trapping of the walnut husk fly, but it didn't appear to be very effective, partly because there were questions about efficacy of the bait.

"We've used some Spinosad-based products for controlling the husk fly, but that's a very expensive treatment," he said, adding that timing is critical.

"With CM you can do Bt—Bacillus thuringiensis—which is a bacterium that paralyzes the gut of the codling moth larvae," Fillmore said.

He said he has seen increasing pressure with NOW, and it is driving him to take a more proactive approach toward that pest in particular, for example with orchard sanitation.

"Certainly, an ounce of prevention is worth a pound of cure," he said, "and especially when it comes to orchard sanitation and controlling NOW."

Knocking mummies out of the tree and mowing them is an important first step, Fillmore said.

Organic processors have very limited options for killing NOW populations after harvest. The main ones are freezing or pasteurization, and both have their own sets of challenges, he said.

Jutta Thoerner, co-owner of Manzanita Manor Organics in Paso Robles, grows about 100 acres of organic, dry-farmed walnuts. She has been farming organically for 25 years and has been certified organic for almost 20 years.

Thoerner plants an organic cover crop every year and said having a really good cover crop is very important for beneficials.

"If you have a nice, strong, blooming cover crop, the beneficials will come. It's just how nature works," she said.

Thoerner agreed there are very few reliable control measures for organic growers. Puffers in her location aren't feasible because of the wind, but she said she has two other control methods she's found effective.

"For probably about 5-6 years, I've used the Peterson female egg trap, which is basically a sticky paper trap," Thoerner said, adding her own research has shown this to be effective in her small operation.

Thoerner said she's also a firm believer in sanitation, and has some unique sanitation measures that have worked well for her.

For example, Thoerner has made use of the wild pigs that go through her orchard.

"They root around and make a big mess under the trees and do a nice little job of soil mixing, and then they eat every single nut that has not been picked up during harvest," she said.

The other helpers are wild turkeys.

"I observed years ago that the wild turkeys will come and go through my hulling pile," Thoerner said, adding that she processes nuts for farmers market and online sales.

"I have shells and I have hulls, and of course that's where navel orangeworm larvae live. And the disposal of that is always tricky for me," she said.

Thoerner makes piles of the shells and hulls, and places them on the outside of the orchard after harvest. Large bands of 40-50 wild turkeys then come and pick through the piles. She provides water for the turkeys and pigs.

Thoerner hasn't had codling moth in her orchard, but she does trap for walnut husk fly, using sticky traps and pheromones. The traps are checked twice a week and the females are counted. If the count is high enough, GF-120 (Spinosad) is applied to the orchard. The last GF-120 application was made about 20 years ago, she said.

Thoerner said she traps every year for walnut husk fly and uses a lot of sticky traps and pheromones.

"It's a lot of manual work," she said, "but it pays off.

"It's the small things. It's hanging a yellow sticky trap with the pheromone that has helped me not to have the walnut husk fly infestation," Thoerner said.

NOW populations in her orchard are stable and not increasing, Thoerner said. Eight or nine years ago, a close neighbor didn't do orchard sanitation, and the following season was the first time she had NOW in her orchard, she said.

"I was very aggressive with my organic methods that I have," Thoerner said, using about 1,000 Peterson sticky traps that year.

Last year and this year, Thoerner said she hasn't seen any NOW, but she continues to trap.

"You cannot let your guard down," she said. "I am so small, I cannot afford to lose even 5% of my harvest. I don't have a gazillion pounds and deep pockets. I have to be very, very proactive."

A team of researchers from University of California Cooperative Extension, the U.S. Department of Agriculture, Chico State University and UC Berkeley received a grant from the California Walnut Board to test eight different combinations of two trap types and four lures, starting in the 2021 season. They will be tested in five walnut orchards in the walnut-producing regions of Lake County, the Sacramento Valley and the northern and central San Joaquin Valley.

(Kathy Coatney is a reporter in Bend, Oregon. She may be contacted at kacoatney@gmail.com.)